In general, coating compositions comprise a carrier liquid, a film forming polymer, a crosslinking (curing) agent, pigments, extenders, and various additives, including but not limited to pigment dispersing agents etc. Pigments are insoluble particles, which are dispersed in the carrier liquid to provide properties such as color, opacity, hardness, durability, and corrosion resistance. Pigments may be natural, synthetic, inorganic, or organic particles, which may be finely ground, such as in the form of a powder. Extenders are fillers for the coating composition that are often used to reduce cost, increase durability, alter appearance, control rheology and may influence other properties of the coating composition. As used herein, the term “pigment” should be understood to include both pigment and extender particles.
The coating of a pigment particle surface with the carrier liquid is referred to as “wetting” or “dispersing” the pigment. The resulting mixture of pigment particles suspended in the carrier liquid is generally referred to as a “pigment dispersion.” If the pigment is not properly dispersed, clusters of pigment particles held together by surface forces may be present. Such a condition is commonly referred to as “agglomeration.” The clusters of pigment particles may be broken up by the application of mechanical forces and stabilized by the addition of pigment dispersants. Pigment dispersants, also known as dispersing agents, increase the stability of a suspension of pigments in a liquid medium. Pigment dispersants also affect the interface between the carrier liquid and the pigment particle, thereby reducing “flocculation”, which is the formation of clusters of pigment particles after the particles have been dispersed.